The present invention pertains to a relatively small, compact compressor and one with an adjustable spacer for varying the performance characteristics.
Relatively small and inexpensive compressors in the range of from 0.5 to 11/2 cubic feet per minute (CFM) capacity have a variety of modern-day applications. Such compressors provide an output pressure nominally ranging from 20 to 60 pounds per square inch (PSIG) and can be used for domestic paint applicating equipment and other relatively light-duty applications. Thus, typically these relatively small compressors are directed to the consumer market, and as such it is necessary to maintain the cost of the units as low as possible for placement in this market.
The head clearance (i.e., the spacing between the top of the piston head employed in the piston-type compressors and the valve plate utilized for controlling the airflow therethrough) has a dramatic effect on the performance characteristics in terms of flow rate at a given pressure. In order to provide a desired flow rate at a duty output pressure, it is necessary to carefully control this clearance; and in the prior art, adjustable shims and precision machining have been employed by the manufacturer to assure the desired performance characteristics. In some cases, it is necessary for the assembly personnel to select a shim, test the unit and substitute a different shim and possibly repeat this process in order to provide the desired performance characteristics. Thus, the assembly operation can add significantly to the overall cost of the unit by increasing the labor involved in assembly of such compressors.
Further, typically the housings and other major structural elements of the compressors have been cast of aluminum; and although preferable to machining, the cast parts are themselves relatively expensive due to the mold costs.